1. Field of the Invention
The present invention relates to a filtration device for filtering a contaminated fluid containing fine particles.
2. Description of the Related Art
A machine tool for precision machining, for example, uses a fluid such as a coolant for lubricating or cooling a part being machined. As the workpiece is machined, fine particles such as dust, carbon, etc., as well as chips, are mixed into the fluid of this type, so that the fluid is gradually polluted and inevitably becomes contaminated.
A filtration device for filtering a contaminated fluid is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-77479. This filtration device uses chips, which are produced from a machine tool, as filter media, and magnetizes the filter media by means of an electromagnetic coil, thereby capturing magnetic impurities in the contaminated fluid.
Since the conventional filtration device described above uses chips as the filter media, its filtration accuracy varies considerably. Since the surfaces of the chips used as the filter media are very rough, moreover, it is difficult to wash the filter media in order to recover the filtration capability when the filtration capability is reduced. Thus, there is a problem that the chips as the filter media must be replaced frequently.
The inventor hereof has developed a filtration device that uses easily washable, spherical magnetic metal balls, such as steel balls, and attracts and fixes the magnetic metal balls by means of a magnet. This filtration device is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-105706. This filtration device has high filtration accuracy and its filter media can be washed with ease.
A filter media unit of the filtration device using the magnetic metal balls includes a filter media accommodation case and a large number of magnetic metal balls contained in the filter media accommodation case. The filter media accommodation case is composed of a pair of mesh members, upper and lower, formed of punching metals (magnetic substance) of iron, a stainless-steel frame member surrounding the mesh members, and the like. However, an earnest investigation by the inventor hereof revealed room for improvement in the conventional filter media unit.
Specifically, if a weak magnet is used in the conventional filter media unit using the magnetic metal balls, attraction of the magnetic metal balls is liable to become unsatisfactory in positions distant from the magnet, although the magnetic metal balls can be fully attracted in positions near the magnet. In consequence, the ability to capture objects to be removed is low in positions distant from the magnet. In the conventional filtration device, for example, a magnetic force obtained at a position farthest from the magnet may sometimes be about a fourth of that obtained near the magnet, so that desired filtration accuracy cannot be obtained, in some cases. Thus, it is necessary to use a larger, stronger magnet. A large, strong magnet, however, requires great drive energy when it is incorporated into or removed from the filter media unit, so that there are problems of enlargement of a drive mechanism and increased energy consumption.